Calibration of Software used for testing purposes


Fully vaccinated are you?
An interesting thread:

>From: Deborah Strauss -

Calibration of Software used for testing purposes is a big issue in my company. Any comments would be appreciated:

how to best do it? how often? R & D software - does it have to be done? (I say yes)

Subject: Re: Q: Cal. of Software Used in Testing/Strauss/Pfrang
Date: Fri, 4 Sep 1998 13:48:12 -0600 From: ISO Standards Discussion

From: pfrang - (Doug Pfrang)
Subject: Re: Q: Cal of Software Used in Testing/Strauss/Pfrang

Every article used on the production floor to manufacture product -- including machines, instruments, chemicals, software-controlled devices, etc. -- has to be validated for its intended purpose. Many articles are validated by brute-force trial-and-error: you experiment with it in your process until you get the process to work the way you want it to; i.e., your products turn out the way you want them to.

Some articles perform a measurement function. For these articles, you have the option of validating the article by having it calibrated; i.e., calibration is one technique of validating the article for its intended purpose. Calibration is not the ONLY technique of validating an article which performs a measurement function, but it is a popular one, because it is often more cost-effective than brute-force trial-and-error validation. Calibration is mainly used when you have a process, formula or recipe that you already know will work (i.e., it has already been validated elsewhere, such as in your R&D department), and you are trying to make sure that your production floor is correctly following that process, formula or recipe. For example, if your process, formula or recipe says to heat something to X degrees for Y minutes, then you want a reliable way of knowing you have heated it to X degrees for Y minutes.

This same rule applies to software-controlled articles used in testing. The first question you ask is, "What is the intended use of this article?" Probably, the intended use of the article is to distinguish good product from bad product. OK, fundamentally, you need to demonstrate that the article has the capability to do this. You have two choices. You can validate the article by brute-force trial-and-error, or you can validate the article by calibrating it.

Validating the article by trial-and-error can be done by collecting many examples of good product and many examples of bad product, running them all through your software-controlled article, and adjusting the article until it passes all the good product and rejects all the bad product.

Validating the article by calibration can be done in the usual way -- comparing it to a recognized standard.

Choose whichever validation technique works and is cheapest in your given application.

How often you revalidate the article (whether it is software-controlled or not) depends on its robustness. First you must determine how long it takes the article to drift so far out of tolerance that it no longer performs its intended use. (This information is often obtained from historical experience with the article.) Once you have this information, you establish your revalidation cycle so you are able to readjust the article before it drifts too far out of tolerance.

Thus, the key to validating software used for testing purposes is to recognize that you do not validate the software, per se; you validate the software-controlled article, and this can be done by brute-force trial-and-error or by calibration.

-- Doug Pfrang --


Software validation

Software validtaion is essential, especially in industries that are regulated by the FDA. The process follows a well defined format. The intention is to guarantee that the system is installed correctly and that the installation is documented (IQ), that the product meets the specifications as claimed (OQ), that the performance of the system meets the process needs (PQ). Professional validations document every stage of the testing. Few calibration software products meet this rigid requirement. Aside from meeting FDA requirements, the process of software validation is beneficial to non-regulated industries. It demonstrates to the buyer that their new sytem is robust, has been developed under strict quality standards and will perform as expected.


itsnick said:
... The process follows a well defined format. ...

Where can I get more information on this "well defined" format for validating software?

My immediate interest is mostly in validating that existing calibration system software is performing calculations correctly. The same is true of existing general-purpose software such as Microsoft Excel. Another interest is when evaluating software to be purchased - verifying that it really performs as intended before we sink the money into it.

I would appreciate additional information, or links to other resources. Thank you.

ben sortin

Use the latest FMEA from the supplier to design the testing for the software.

You are only as good as your worst data set.

Make sure that you have properly defined the system and terms with the person or organization that is requiring "software calibration".

I spent 4 hours trying to explain to a certain auditor from a nuclear power plant that we didn't have the required tractor-trailer load of engineering data to satisfy him that the software for our measurement instrument was "calibrated".

After finally walking him through the process that produced the measurement instrument, he was satisfied. Here's why: every instrument was fed NIST traceable signals for the values shown as calibrated on the certificate that shipped with the unit. By proving that instrument correctly translated the XYZ signal input to an XYZ display that was human readable, we had validated that the software was "calibrated".


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